First off I dont think Mother was a Smoke Monster, nor do I think that MIB was the first Smoke Monster.
I think that the Smoke Monster was the guard dog to the protector of the island being able to be summoned upon command to do their bidding...we see this with how Mother was able to destroy the village.
The ability of the Smoke Monster being able to be seen as dead people is just one of the fringe benefits. How this happens still not sure....but I am leaning to the ability to control the human brain and making people see what they want to see.
Now up until Jacob threw MIB down into the light the Smoke Monster was a creature without a mind of its own...its only purpose was to do the bidding of the protector. Basically it was a slave.....The Mother said that to go down into the light would be a fate worse then death...the only thing I can thing of that is worse then death is to live in bondage. So the Smoke Monster is a slave that knows of nothing except to serve....until
Jacob throws MIB down into the light. And MIBs thoughts perhaps even his soul become one with the Monster and now the Monster has a not a new purpose but I new view on his life because he now sees the world through MIBs eyes and not the eyes of a slave!